Audio amplifier performance while maintaining usb compliance and power down protection

ABSTRACT

An apparatus comprises a first audio amplifier circuit configured to provide an analog audio signal and an analog switch circuit including a first input configured to receive the analog audio signal, a second input configured to receive a first digital data signal, and a first output configured to provide one of the digital data signal or the analog audio signal. The apparatus also includes a first feedback circuit coupled to the first audio amplifier circuit and the analog switch circuit output, the feedback circuit configured to bias the first audio amplifier circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.12/790,122, filed on May 28, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND

Personal electronic devices include MP3 portable media players, cellularphones, and smart phones. Popularity of the devices stems in part fromthe functionality they provide despite their small size. It is desirableto continue to provide more functionality in such devices even though itis desired to keep the devices at their same small size or to make themeven smaller.

OVERVIEW

This document relates generally to electronic devices, and morespecifically to providing combined audio and data capability in portableelectronic devices. In example 1, an apparatus includes a first audioamplifier circuit configured to provide an analog audio signal, and ananalog switch circuit. The analog switch circuit includes a first inputconfigured to receive the analog audio signal, a second input configuredto receive a first digital data signal, and a first output configured toprovide one of the digital data signal or the analog audio signal. Theapparatus also includes a first feedback circuit coupled to the firstaudio amplifier circuit and the analog switch circuit output. Thefeedback circuit is configured to bias the first audio amplifiercircuit.

In example 2, the apparatus of example 1 optionally includes a secondaudio amplifier circuit. The first audio amplifier circuit and thesecond audio amplifier circuit optionally provide analog audio signalsfor right and left audio channels. The analog switch circuit includes athird input communicatively coupled to an output of the second audioamplifier circuit, a fourth input configured to receive a second digitaldata signal, and a second output, wherein the first and second outputsprovide one of the first and second data signals or the analog audiosignals for right and left audio channels. The apparatus of example 1optionally includes a second feedback circuit communicatively coupled tothe second audio amplifier circuit and the second analog switch circuitoutput. The second feedback circuit is configured to bias the secondaudio amplifier circuit.

In example 3, the first data signal and the second data signal ofexample 2 optionally form a complementary digital signal pair.

In example 4, the apparatus of any one of claims 1-3 optionally includesa communication port communicatively coupled to the analog circuitswitch output.

In example 5, the communication port of example 4 optionally includes auniversal serial bus (USB) port.

In example 6, the analog circuit switch of any one of examples 4 and 5optionally includes a select input, wherein a change of state of theselect input changes the communication port between a digital data modeand an analog audio mode.

In example 7, the feedback circuit of any one of examples 4-6 optionallyincludes a second switch circuit communicatively coupled to thecommunication port and configured to disconnect the feedback circuitpath from the communication port when the analog switch circuit providesthe digital data signal.

In example 8, the apparatus of example 7 optionally includes a pseudovoltage supply circuit. The pseudo voltage supply circuit is configuredto derive a pseudo-voltage supply from a connector of the communicationport and provide the pseudo-voltage supply to the analog switch circuitand the second switch circuit.

In example 9, the second switch circuit of any one of examples 7 and 8optionally includes a complementary metal oxide (CMOS) pass-gatecircuit. The pseudo-voltage supply is provided to the pass-gate circuitwhen the analog switch circuit provides the analog audio signal to thecommunication port.

In example 10, a method includes multiplexing, with a multiplexingcircuit, one of a first electrical digital data signal and a firstelectrical analog audio signal to a connector of a communication port,and incorporating the multiplexing circuit in a first feedback circuitpath used to bias an audio amplifier circuit that generates the firstanalog audio signal.

In example 11, the multiplexing of example 10 optionally includesmultiplexing the first digital data signal and the first analog audiosignal to a connector of a digital data port.

In example 12, the method any one of examples 10 and 11 optionallyincludes connecting the first feedback circuit path when providing thefirst analog audio signal to the connector of the communication port anddisconnecting the feedback circuit path when providing the first digitaldata signal to the connector of the communication port.

In example 13, the multiplexing of any one of examples 10-12 optionallyincludes multiplexing one of a second electrical digital data signal anda second electrical analog audio signal to a second connector of acommunication port. The incorporating the multiplexing circuit ofexamples 10-12 optionally includes incorporating the multiplexingcircuit in a second feedback circuit path used to bias a second audioamplifier circuit that generates the second analog audio signal. Thefirst and second digital data signals are optionally a complementarydigital signal pair, and the first and second analog audio signalsoptionally correspond to right and left audio channels.

In example 14, the communication port of any one of example 10-13optionally includes a USB port. The multiplexing of the examplesoptionally includes multiplexing the complementary digital signal pairto connectors of the communication port when the communication portoperates in USB mode and multiplexing the right and left audio channelsto the connectors of the communication port when operating the USB portin an audio mode.

In example 15, an integrated circuit (IC) includes a first IC output, afirst audio amplifier circuit configured to provide an analog audiosignal, and an analog multiplexer (mux) circuit. The analog mux circuitincludes a first input configured to receive the analog audio signal, asecond input configured to receive a first digital data signal, and afirst output configured to provide one of the first digital data signalor the analog audio signal to the first IC output. The IC optionallyincludes a first feedback circuit path from the analog mux circuitoutput to an input of the first audio amplifier circuit, wherein thefeedback circuit is configured to bias the first audio amplifiercircuit.

In example 16, the first IC output of example 15 is optionallyconfigured to be communicatively coupled to a digital data port.

In example 17, the first digital data signal of any one of examples 15and 16 optionally complies with a digital data port communicationprotocol. The analog mux circuit of the examples optionally includes aselect input and the first analog mux circuit output is optionallyconfigured to provide one of the analog audio signal or thecommunication protocol compliant digital data signal at the first muxoutput according to a state of the select input.

In example 18, the IC of anyone of examples 15-17 optionally includes asecond IC output and a second audio amplifier circuit. The first audioamplifier circuit and the second audio amplifier circuit optionallyprovide analog audio signals for right and left audio channels. Theanalog mux circuit of the examples optionally includes a third inputcommunicatively coupled to an output of the second audio amplifiercircuit, a fourth input to receive a second digital data signal, and aselect input. The first digital data signal and the second digital datasignal are optionally a complementary data signal pair. The secondoutput is optionally communicatively coupled to the second IC output,and the first and second analog mux circuit outputs provide one of thecomplementary data signal pair or the analog audio signals for the rightand left audio channels to the first and second IC outputs according tothe state of the select input. The IC further optionally includes asecond feedback circuit path from the second analog mux circuit outputto an input of the second audio amplifier circuit.

In example 19, the feedback circuit path of any one of examples 15-18optionally includes a switch circuit communicatively coupled to thefirst IC output. The switch circuit is optionally configured todisconnect the feedback circuit path from the first IC output when theanalog mux circuit provides the digital data signal to the first ICoutput and connect the feedback circuit path and provide the audiosignal to operate in an audio mode.

In example 20, a first voltage supply circuit is applied to the firstaudio amplifier circuit of any one of examples 15-19. A second voltagesupply circuit is optionally applied to the switch circuit to connectthe feedback circuit path to the first IC output when the analog muxcircuit provides the analog audio signal to the first IC output.

This section is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a block diagram of portions of an example of a device toprovide both data and audio to a single port.

FIG. 2 is a block diagram of portions of an example of another device toprovide both data and audio to a single port.

FIG. 3 is circuit schematic of an example of a disconnect switchcircuit.

FIG. 4 is a flow diagram of an example of a method of providing combinedaudio and data capability using a digital data port.

FIG. 5 shows a simulation of the analog signal seen at the output of ananalog switch circuit.

DETAILED DESCRIPTION

This document relates generally to electronic devices and in particular,to incorporating audio capability into a digital data port. As explainedabove, it is desired to improve functionality of portable electronicdevices despite the pressure to provide the functionality in a smalldevice size.

The ability to reduce the size of a device is typically limited by thephysical size of the user interfaces it includes. For example, aportable electronic device may be limited by the physical size of adisplay, keypad, or device ports. One way to provide the functionalityin a small device size is to increase the functionality of the remainingdevice interfaces.

FIG. 1 is a block diagram of portions of an example of a device 100 toprovide both data and audio to a single port. The port can be a digitaldata port or a data communication port. Examples of a digital data portinclude, among other things, a universal serial bus (USB) port, a videodata port, a camera data port, or a high definition multimedia interface(HDMI). The digital data for the port can be provided by a separatedigital device or digital subsystem of the same device.

The device 100 includes an audio amplifier circuit 105. The audioamplifier circuit 105 provides an electrical audio analog signal. Theaudio analog signal is an amplified signal derived from an input to theaudio amplifier circuit 105. The audio analog signal includes afrequency or frequencies in the audio range and the amplitude of thesignal can vary to be any value between a maximum voltage and a minimumvoltage.

The device 100 includes an analog switch circuit 110 in series with theoutput of the audio amplifier circuit and the port. The analog switchcircuit 110 includes a first input 112 to receive the analog audiosignal, a second input 114 to receive the digital data signal. Thedigital data signal complies with a communication protocol of thedigital data port, such as a communication protocol for any of the dataports listed above for example.

The analog switch circuit 110 includes an output 115 to provide one ofthe digital data signal or the analog audio signal. The output 115 isable to provide continuous levels of output voltage of an analog signalin addition to the discrete levels of the digital data signal. Theanalog switch circuit 110 also provides isolation of the output 115 fromthe inputs. The analog switch circuit output 115 can be communicativelycoupled to a port connector. The communicative coupling allows theanalog switch circuit 110 to communicate signals to the port even thoughthere may be intervening circuitry.

In some examples, the analog switch circuit 110 includes a multiplexer(mux) circuit. Multiplexing the analog audio signal and the digital datasignal allows use of the digital data port as both a data port and anaudio port. In some examples, the analog circuit switch includes aselect input. A change of state of the select input (e.g., low to high,or inactive to active) changes the mode of the communication portbetween a digital data mode and an analog audio mode. For example, theport connector may a pin connector designated as a data pin connectorfor a USB port. A speaker (e.g., a set of headphones) could be connectedto the USB port with a USB connector, and audio signals could beprovided to the speaker via the data pin. The select input changes theUSB port mode between data and audio. In some examples, the presence ofthe speaker connection is sensed by the device 100 (e.g., by a sensedimpedance) and the select input is set to provide the audio mode.

The analog switch circuit 110 is able to isolate the audio amplifiercircuit 105 from the port connector when providing a digital data signalto the port connector. Isolating the audio amplifier circuit 105regulates the capacitance seen at the port when data is transmitted orreceived. Without the isolation, the capacitance seen at the port maybecome too great to ensure compliance with timing of the digitalcommunication protocol used by the port.

Adding the analog switch circuit in series with the output of the audioamplifier circuit 105 and the port may have detrimental effects on thequality of the audio amplifier circuit 105 as seen at the portconnector. This series arrangement may reduce the signal gain, theoutput power, and the total harmonic distortion (THD) of the performanceof the audio amplifier circuit 105 seen at the port connector.

The analog switch circuit 110 also includes a feedback circuit 120coupled to the audio amplifier circuit 105 and the analog switch circuitoutput 110. It can be seen in the Figure that the feedback circuit 120includes a feedback loop incorporating the analog switch circuit 110 andthe biasing impedance 125 of the audio amplifier circuit 105. Thefeedback circuit 120 incorporates the impedance of the analog switchcircuit 110 to bias the audio amplifier circuit. By including the analogswitch circuit 110 in the feedback path, the signal gain, the outputpower, and the THD of the audio amplifier circuit are all improved.

However, the feedback circuit 120 may increase the impedance seen at theport connector to the point where power down protection and data signalcompliance with the port protocol may be compromised. In order to ensureprotocol compliance and power down protection, the feedback circuit 120includes a second switch circuit 130 communicatively coupled to thecommunication port and configured to disconnect the feedback circuitpath from the communication port when the analog switch circuit 110provides a digital data signal.

In some examples, the device is formed of multiple components on aprinted circuit board. In some examples, the device is provided on anintegrated circuit (IC). The output of the analog switch circuit 110 canbe communicatively coupled to an IC output, and the IC output iscommunicatively coupled to a port connector.

FIG. 2 is a block diagram of portions of an example of another device200 to provide both data and audio to a single port. The device 200includes a first audio amplifier circuit 205 and a second audioamplifier circuit 255. The outputs of audio amplifier circuits areprovided to an analog switch circuit 210. The analog switch circuit 210includes two inputs (212A, 212B) to receive an analog audio signal fromeach of the first and second audio amplifier circuits. In some examples,the first audio amplifier circuit 205 provides an analog audio signalcorresponding to a left audio channel signal and the second audioamplifier circuit 255 provides an analog audio signal corresponding to aright audio channel signal. The left and right audio channels mayprovide stereo signals for a set of headphones.

The analog switch circuit 210 also includes two inputs (214A, 214B) toreceive two digital data signals. In some examples, the first and seconddigital data signals are provided by a digital subsystem (not shown)included in the device 200. The analog switch circuit also includes twooutputs. In some examples, the outputs are communicatively coupled totwo connectors of a communication port. In some examples, the device 200is incorporated into an IC and the outputs are communicatively coupledto IC outputs (I0, I1 as shown). The IC outputs are then communicativelycoupled to connectors of a communication port, such as a digital dataport.

In some examples, the analog switch circuit 210 includes a select input.A change of state of the select input changes the signals at the outputsbetween the digital data signals (for a digital data mode) and theanalog audio signals (for an analog audio mode). In some examples, theanalog switch circuit 210 includes a separate analog enable (a_en) and aseparate data enable (d_en) to provide one of the data signal pair orthe analog signal pair at the output. In some examples, if neither theanalog signals nor the digital data signals are enabled, the outputs ofthe analog switch are in a high impedance state. This may allow datasignals to be received on the outputs and communicated to a digital datasubsystem.

In some examples, the first data signal and the second data signal forma complementary digital signal pair, such as the complementary datasignals (D+, D−) for a USB connector. The outputs of the complementarydata signal pair or the analog audio signals for right and left audiochannels are provided to the IC outputs and/or the communication portconnectors according to the state of the select input (or the states ofthe enables).

The device 200 includes a first feedback circuit 220 communicativelycoupled to the first audio amplifier circuit 205 and the first output ofthe analog switch circuit 210. The first feedback circuit 220 biases thefirst audio amplifier circuit 205 and includes a feedback loopincorporating the analog switch circuit 210 and the biasing impedance225 of the first audio amplifier circuit 205. The device 200 alsoincludes a second feedback circuit 270 communicatively coupled to thesecond audio amplifier circuit 255 and the second output of the analogswitch circuit 210. The second feedback circuit 270 biases the firstaudio amplifier circuit 205 and includes a feedback loop incorporatingthe analog switch circuit 210 and the biasing impedance 275 of thesecond audio amplifier circuit 255.

Each of the feedback circuits also includes a switch circuit (230, 280)communicatively coupled between its analog circuit output and its audioamplifier input. The switches are configured to disconnect the feedbackcircuit paths from the device output when the analog switch circuit 210provides the digital data signals and connect the feedback circuit pathswhen the analog switch circuit 210 provides the analog audio signals.

As explained previously, the disconnect switch circuit needs todisconnect its feedback circuit path from the external I/O pad or pinconnection to ensure that the digital data signals comply with acommunication protocol and to provide power down protection. To providethis protection, the disconnect switch circuits need to be supplied witha separate voltage supply rail, or a pseudo voltage supply rail.

FIG. 2 shows the pseudo voltage supply rail (prail) as generated by apseudo voltage supply circuit in the analog switch circuit cell. Thepseudo voltage supply rail provides power to the disconnect switchcircuits when the circuit supply (Vcc) is 0V and a DC voltage is appliedto the communication port. The pseudo voltage supply circuit derives apseudo-voltage supply from a connector of the communication port andprovides the pseudo-voltage supply to the analog switch circuit and thedisconnect switch circuits. The voltage of the pseudo voltage supplyrail may be greater than the circuit supply (Vcc). Using the pseudovoltage supply rail for the disconnect switches ensures that parasiticdiodes will not forward bias when the communication port is stressedduring power down. An approach for generating a pseudo voltage supplyrail can be found in Miske et al., U.S. Pat. No. 6,163,199,“Overvoltage/Undervoltage Tolerant Transfer Gate,” filed Jan. 29, 1999,which is incorporated herein by reference in its entirety.

FIG. 3 is circuit schematic of an example of a disconnect switch circuit300. The disconnect switch circuit 300 includes a complementary metaloxide (CMOS) pass-gate circuit 305.

In the Figure, when Vcc is 0V, the pseudo voltage supply rail, prail isprovided by the inverter 310 to the PMOS transistor and 0V (Vcc) isprovided to the NMOS transistor to deactivate or disconnect thepass-gate circuit 305. Thus, when Vcc=0V, prail is provided to theswitch when the device is powered down or when it is desired to providethe data signals to the communication port. When Vcc is high, Vee (e.g.,ground) is provided to the PMOS transistor and Vcc is provided to theNMOS transistor to activate the pass-gate circuit 305 and to connect thefeedback circuit path.

FIG. 4 is a flow diagram of an example of a method 400 of providingcombined audio and data capability with a digital data port. At block405, one of a first electrical digital data signal and a firstelectrical analog audio signal are multiplexed to a connector of acommunication port using a multiplexer circuit. In some examples, themultiplexing includes multiplexing the first digital data signal and thefirst analog audio signal to a connector of a digital data port. Atblock 410, the multiplexing circuit is incorporated in a first feedbackcircuit path used to bias an audio amplifier circuit that generates thefirst analog audio signal.

In some examples, the method 400 includes connecting the first feedbackcircuit path when providing the first analog audio signal to theconnector of the communication port and disconnecting the feedbackcircuit path when providing the first digital data signal to theconnector of the communication port. As explained above, this is usefulto maintain compliance of the data signals for the protocol of thedigital data port. Having too great a capacitive load may result inhaving to run the port at too slow a speed.

According to some examples, the method 400 further includes multiplexingone of a second electrical digital data signal and a second electricalanalog audio signal to a second connector of a communication port. Inother words, either two digital data signals, or two analog audiosignals are multiplexed to first and second connectors of thecommunication port. The multiplexing circuit is incorporated into asecond feedback circuit path used to bias a second audio amplifiercircuit that generates the second analog audio signal. Examples of thefirst and second feedback circuit paths are shown in FIG. 2.

In some examples, the first and second analog audio signals correspondto right and left audio channels to provide stereo audio signals to thecommunication port. In some examples, the first and second digital datasignals are a complementary digital signal pair. As discussedpreviously, the communication port can include a USB port. Thus, themethod can include multiplexing the complementary digital signal pair toconnectors of the communication port when the communication portoperates in USB mode and multiplexing the right and left audio channelsto the connectors of the communication port when operating the USB portin an audio mode.

Including a multiplexer circuit or an analog switch circuit in thefeedback path used to bias the audio amplifiers can improve signal gain,output power, and THD of the audio circuit. FIG. 5 shows a simulation ofthe analog signal seen at the output of the analog switch circuit 110 ofFIG. 1. The simulation includes an output analog signal 505 resultingfrom not including the analog switch circuit 110 to the feedback pathused to bias the audio amplifier circuit 105. The simulation shows thatthe voltage amplitude of the output analog signal 505 is less than theinput signal 510; resulting in a gain of −0.45 decibels (dB). Thesimulation also shows an output analog signal 515 with the impedance ofthe analog switch circuit 110 added to the feedback path that biases theaudio amplifier circuit 105. The simulation shows that the voltageamplitude of the output analog signal 515 is slightly greater than theinput signal 510; resulting in a gain of +0.009 dB.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects. Methodexamples described herein can be machine or computer-implemented atleast in part.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An integrated circuit (IC) comprising: a first ICoutput; a first audio amplifier circuit configured to provide an analogaudio signal; an analog multiplexer (mux) circuit including: a firstinput configured to receive the analog audio signal; a second inputconfigured to receive a first digital data signal; and a first outputconfigured to provide one of the first digital data signal or the analogaudio signal to the first IC output; and a first feedback circuit pathfrom the analog mux circuit output to an input of the first audioamplifier circuit, wherein the feedback circuit is configured to biasthe first audio amplifier circuit.
 2. The IC of claim 1, wherein thefirst IC output is configured to be communicatively coupled to a digitaldata port.
 3. The IC of claim 1, wherein first digital data signalcomplies with a digital data port communication protocol, and whereinthe analog mux circuit includes a select input and the first analog muxcircuit output is configured to provide one of the analog audio signalor the communication protocol compliant digital data signal at the firstmux output according to a state of the select input.
 4. The IC of claim1, including: a second IC output; a second audio amplifier circuit,wherein the first audio amplifier circuit and the second audio amplifiercircuit provide analog audio signals for right and left audio channels,wherein the analog mux circuit includes: a third input communicativelycoupled to an output of the second audio amplifier circuit; a fourthinput to receive a second digital data signal, wherein the first digitaldata signal and the second digital data signal are a complementary datasignal pair; a select input; and a second output communicatively coupledto the second IC output, wherein the first and second analog mux circuitoutputs provide one of the complementary data signal pair or the analogaudio signals for the right and left audio channels to the first andsecond IC outputs according to the state of the select input, andwherein the IC further includes a second feedback circuit path from thesecond analog mux circuit output to an input of the second audioamplifier circuit.
 5. The IC of claim 1, wherein the feedback circuitpath includes a switch circuit communicatively coupled to the first ICoutput, wherein the switch circuit is configured to: disconnect thefeedback circuit path from the first IC output when the analog muxcircuit provides the digital data signal to the first IC output; andconnect the feedback circuit path and provide the audio signal tooperate in an audio mode.
 6. The IC of claim 5, wherein a first voltagesupply circuit is applied to the first audio amplifier circuit, andwherein a second voltage supply circuit is applied to the switch circuitto connect the feedback circuit path to the first IC output when theanalog mux circuit provides the analog audio signal to the first ICoutput.